Method and apparatus for imaging and analysis of corneal tissue

ABSTRACT

A method and accompanying apparatus are provided for in vivo imaging of corneal tissue. In general, the method comprises providing a laser beam having a substantially planer configuration. The substantially planar laser beam is directed through a cross-sectional portion of the cornea of a patient, so as to illuminate the cross-sectional portion and cause the laser beam to be scattered by molecules in the corneal tissue. Then, at least a portion of the scattered laser light is detected so as to form a cross-sectional image of the corneal tissue. In general, the planar configured laser beam will have a slit-like cross-sectional dimension having essentially the same width dimension over the depth of field within which the largest depth dimension of the eye extends. These unique characteristics of the illumination beam permit the formation of clear, in-focus images detected at the image detection plane. The method and apparatus of the present invention can be used for objectively measuring the optical density of corneal tissue, as well as precisely measuring the physical dimensions, such as thickness and curvature, of the cornea and its correct spatial relationship within the eye. The method and apparatus of the present invention can be utilized to produce in-focus cross-sectional images, from which the optical density of corneal tissue can be precisely measured and thus the precise degree and location of corneal haze therewithin determined. Also, corneal thickness and topographical data can be produced for use by ophthalmological surgeons in planning the precise curvature profile that must be photo-ablatively sculptured in the stroma tissue of a particular patient in order to achieve a desired degree of optical correction in his or her eye.

RELATED CASE

This is a continuation-in-part application of application Ser. No.07/604,661, entitled "Method And Apparatus For Imaging And Analysis OfOcular Tissue" filed on Oct. 26, 1990, now U.S. Pat. No. 5,139,022,incorporated herein by reference.

FIELD OF INVENTION

The present invention generally relates to a method and apparatus forobjectively assessing in vivo the properties of ocular tissue, and moreparticularly to a method and apparatus for in vivo imaging and analysisof corneal tissue in an objective and quantitative manner for diagnosticand therapeutic purposes.

BACKGROUND OF INVENTION

In many diagnostic and therapeutic applications, there is great need toobjectively quantify the optical density, shape and size of variousocular tissue, such as the crystalline lens and cornea.

Regarding the cornea lens, it is well known that the presence of cornealhaze at particular locations on the cornea can effect, in particularindividuals, the visual acuity and function of the eye. It is also knownthat the optical density of the corneal haze is related to the amount oflight diffusion (i.e. scatter) caused by increased size and coagulationof protein molecules in the cornea. Presently, prior art descriptions ofcorneal haze have generally consisted of a morphologic statement. Suchmorphologic descriptions have been based primarily on the patient'spotential visual acuity estimated using an acuity scope.

A number of techniques have been developed over recent years forachieving desired refraction-corrective surgery in the human eye bylaser sculpturing the optically used portion of the cornea. Examples ofsuch prior art techniques are disclosed in U.S. Letters Patent Nos.4,718,418; 4,732,148; 4,773,414; 4,729,372; 4,669,466; 4,473,330;4,856,513; and 4,994,058. While some of these U.S. Letters patentsutilize different forms of apparatus, they each disclose essentially thesame method for photoablative laser sculpture of the cornea.

In general, the preoperative step of the method involves removing theepithelial layer from central anterior area of the cornea. Then anultraviolet laser beam of a controlled cross-sectional diameter isdirected to the epithelium free area for uniform photoablation throughthe Bowman's membrane and selective penetration of the stroma, achievinga new curative profile of predetermined characteristics solely in stromatissue. Thereafter, post operative procedures favorable to smoothefficient epithelial regrowth over the surgically sculptured region areperformed. As it is not presently uncommon for a certain amount ofcorneal "haze" or light scattering to result from the laser sculpturingprocedure, which may be more or less noticeable in different patients,post-operative treatment of this disorder is also typically performedusing a variety of typically applied drugs.

Prior to performing the corneal sculpturing procedure described above,it is important to acquire data representative of thickness andtopography of the cornea of a particular abnormal eye. Such data must bein the form of a readily interpretable context against which the depthand surface distribution of the surgical incision into the anteriorsurface of the abnormal cornea can be determined in order to achieve adesired refractive correction in the patient's eye. In addition, formedical and legal documentation purposes, it is important for theophthalmological surgeon to objectively determine and record the precisedegree of corneal haze present in the patient's eye prior to and afterlaser sculpture of the cornea.

U.S. Pat. No. 4,669,466 discloses a CAD/CAM system for use in acquiringcorneal topographical and thickness data which can be used by theophthalmological surgeon in determining the new curvature profile to beformed in the stroma in order to achieve a desired degree of opticalcorrection in the patient's eye. Equipment presently used for acquiringcorneal topographical data includes an optical ocular scanner or aphotokeratometer with provision for generating digitized topographicaldata. Exemplary of this equipment is the PFS-1000 photokeratoscopecommercially available from the Japanese firm, Sun Contact Lens Co.,Ltd., with U.S. offices in Palo Alto, California. The Sunphotokeratoscope has the ability to rapidly scan the cornea in such away as to determine the entire topography of the outer surface of thecornea, from limbus to limbus. Subtle differences in curvature of theouter cornea or inner optical zone are precisely and clearly defined.The photokeratoscope is available with a photoanalyzer having thecapability of digitizing the data from thousands of individual points onthe particular cornea, and producing a digitized output, from which avisual display is producible to show the cross-sectional profile ofanterior-surface curvature for any cross-sections which include thecentral axis of the eye.

Equipment presently used for acquiring corneal thickness data includespachymeter for making multiple determinations of the precise thicknessof the cornea, to within thousandths of a millimeter, at plurallocations on the surface of the cornea. Using ultrasonic-ranging,measured thickness data correlated with location-coordinate data isprovided as digitized output. The pachymeter measurements may beperformed manually on an individual point-by-point basis, using acommercially available hand-held transducer probe flexibly connected topower supply and display means, for example the Myopach ultrasonicpachymeter available from Myocure, Inc., Los Angeles, California, or the"Villasenor" ultrasonic pachymeter, available from Cilco, Inc.Huntington, W. Virginia. In using such a device, a fixation targetenables the unexamined eye of the patient to maintain central-axisstability for his examined eye when the probe is placed on the cornealsurface anywhere from the central optical axis to the periphery.

While the above-described equipment has the capability of acquiringtopographical and thickness data of the cornea, the nature of this datais approximate as it has been generated on the basis of a fixed numberof measurements made at points along the surface of the cornea and thenapplying mathematical estimation techniques.

Thus, there is great need for a method and apparatus that is capable ofproducing objective measurements of corneal haze and determining the 3-Dgeometry of the cornea and associated structures in a way which is freefrom the shortcomings and drawbacks accompanying the prior art.

Accordingly, it is primary object of the present invention to provide amethod and apparatus for in vivo imaging and analysis of corneal tissuein an objective, quantitative manner.

It is a further object of the present invention to provide such a methodand apparatus, from which cross-sectional images of corneal tissue canbe formed over a high depth of field extending far beyond the thicknessof the cornea and crystalline lens.

A further object of the present invention is to provide such a methodand apparatus, from which accurate cross-sectional images of cornealtissue can be formed, with correct spatial relationships between ocularstructures.

A further object of the present invention is to provide a method andapparatus for precisely measuring the physical dimensions of the corneaand its correct spatial relationships within the eye.

An even further object of the present invention is to provide a methodand apparatus for forming cross-sectional images of corneal tissue whichenable precise localization of zones of increased optical density, suchas corneal haze.

Yet a further object of the present invention is to provide alaser-based corneal tissue analysis system in which cross-sectionaldigital images of the cornea, crystalline lens and surrounding ocularstructures can be formed and from which the precise degree and locationof optical density of the cornea can be objectively determined usingdigital image analysis.

A further object of the present invention is to provide such a cornealtissue analysis system in which the luminance and cross-sectionaldimension of the laser illumination used to visualize the lens and formcross-sectional corneal images, can be maintained essentially uniformlyconstant from image to image, and photo-examination session tophoto-examination session.

A further object of the present invention is to provide such a cornealtissue analyzing system which includes a microscope and an imagedetector that uses laser illumination for visualizing and formingperfectly focused cross-sectional images entirely through the outertissue comprising the cornea and crystalline lens.

An even further object of the present invention is to provide alaser-based corneal tissue analysis system in which 3-D model of thecornea and its surrounding ocular structures in the eye can be generatedusing cross-sectional digital images formed of these structures.

These and other objects of invention will become apparent hereinafterand in the claims.

SUMMARY OF INVENTION

According to one of broader aspects of the present invention, a methodand accompanying apparatus are provided for in vivo imaging of cornealtissue. In general, the method comprises providing a laser beam having asubstantially planer configuration. The planar laser beam is directedthrough a cross-sectional portion of the corneal tissue, so as toilluminate the cross-sectional portion and cause the laser beam to bescattered by molecules in the corneal tissue. Then, at least a portionof the scattered laser light is detected so as to form a cross-sectionalimage of the corneal tissue.

In general, the planar configured laser beam has a slit-likecross-sectional dimension having substantially the same width dimensionover the depth of field within which the largest depth dimension of theeye extends. These unique characteristics of the illumination beampermit the formation of clear, in-focus images detected at the imagedetection plane.

The method and apparatus of the present invention can be used forobjectively measuring the optical density of ocular tissue, as well asprecisely measuring the physical dimension of ocular structures andtheir correct spatial relationships within the eye.

In the case of the cornea, the method and apparatus of the presentinvention can be utilized to produce in-focus cross-sectional images,from which the optical density of tissue forming the cornea can beprecisely measured and thus the precise degree of and location ofcorneal haze therewithin determined.

In the case of the crystalline lens, the method and apparatus of thepresent invention can be utilized to produce in-focus cross-sectionalimages, from which the optical density of tissue comprising the lens canbe precisely measured and thus the precise degree and location ofcataract therewithin determined.

In the illustrated embodiment, the apparatus of the present invention isrealized in the form of an ocular tissue analysis system, which iscapable of forming a plurality of cross-sectional images of the cornealtissue, with each image being specified at a different light scatterplane, defined within the corneal tissue. Preferably, the corneal tissueanalysis system comprises illumination beam directing means fordirecting the planar laser beam into the ocular tissue at a selectedangle of incidence with respect to the corneal tissue, so that, for eachselected angle of incidence, the laser light scatters principally in adifferent light scatter plane within the corneal tissue. The system alsoincludes detecting means for detecting a portion of the scattered laserlight from each different light scatter plane. On the basis of theplurality of acquired cross-sectional images, a three-dimensional imageor model of the corneal tissue can be reconstructed and subsequentlydisplayed along desired viewing directions.

From the three-dimensional image model of the cornea, the physicalthickness of the cornea can be accurately determined at each point alongthe surface of the cornea. Also, from the three-dimensional image modelof the cornea, its topography (i.e., surface characteristics) can beaccurately determined. Corneal thickness and topographical data (i.e.corneal curvature) obtained from the three-dimensional image model ofthe cornea can then be used by the ophthalmological surgeon in planningthe precise curvature profile that must be photoablatively sculptured inthe stroma tissue of a particular patient in order to achieve a desireddegree of optical correction in his or her eye.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the objects of the present invention, thedetailed description of the illustrated embodiment is to be taken inconnection with the following drawings, wherein:

FIG. 1A is a schematic representation of the method of image formationaccording to the present invention, showing the illumination of across-sectional portion of a crystalline lens with a substantiallyplanar laser beam of substantially uniform luminance and the detectionof scattered laser light from the cross-sectional portion to form animage thereof at the image detection plane;

FIG. 1B is a schematic representation of the method of the presentinvention, illustrating the path of laser illumination and light scatterand detection, as viewed from along the Z-Y plane of the coordinatereference system of FIG. 1A;

FIG. 2 is a schematic representation of the first embodiment of thepresent invention realized as a binocular microscopic and scatter imagedetection and analysis system;

FIG. 3A is a schematic representation of a detailed scatter image of across-sectional portion of the eye shown in FIG. 1B, taken along line2A--2A, representative of the central portion of the cornea and thecrystalline lens;

FIG. 3B is a schematic representation of a detected scatter image of across-sectional portion of the eye shown in FIG. 1B, taken along line2B--2B, representative of an edge portion of the cornea and crystallinelens;

FIG. 4 is a schematic representation of a detected scatter image formedin accordance with the method of the present invention, illustrating thevarious ocular structures within the image and the use of digital imageprocessing to provide the luminance (i.e., optical density) profilealong a selected line of analysis;

FIG. 5 is a schematic representation of the second embodiment of theapparatus of the present invention, realized as an ocular tissueanalyzing system including a binocular microscope and scatter imagedetection and analyzing subsystem capable of forming a plurality ofcross-sectional images of ocular tissue taken at different angles ofillumination incidence, and reconstructing these cross-sectional imagesto form a three-dimensional image of the cornea, crystalline lens andsurrounding ocular structures;

FIG. 5A is a schematic representation of the second embodiment of theapparatus of the present invention, as view from along X-Z plane of thecoordinate reference system of FIG. 5; and

FIG. 6 is schematic representation of the third embodiment of theapparatus of the present invention, realized as an ocular tissueanalyzing system including a binocular microscope and scatter imagedetection and analyzing subsystem capable of forming a plurality ofcross-sectional images of the cornea and crystalline lens taken atdifferent angles of illumination incidence, and reconstructing thesecross-sectional images to form a three-dimensional image of the corneaand the crystalline lens.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

Referring to FIGS. 1A and 1B in particular, the method of in vivoimaging ocular tissue according to the present invention, will first bedescribed.

According to the present invention, a laser beam is used to illuminateocular tissue so that laser light scattered by molecules comprising thetissue can be detected on an image detection plane positioned at somepreselected scatter angle. An essential characteristic of theillumination laser beam of the present invention is that it has asubstantially planar configuration and a substantially uniform luminanceover each slit-like cross-section.

It has been discovered that by using a substantially planar laser beamhaving a substantially uniform luminance over each slit-likecross-section, wherein the width of each slit-like cross-section issubstantially constant along the planar laser beam, it is possible toilluminate ocular tissue within the eye with a flux density which doesnot diverge along the depth of field, within which the largest depthdimension of the eye extends. Consequently, light scattered from oculartissue anywhere along the propagation direction of the planar laserbeam, will provide clear in-focus images detected at the image detectionplane.

Generation of a substantially planar laser beam in accordance with theprinciples of the present invention can be achieved using a commerciallyavailable zoom laser diode line projector system, such as ModelV-SLM-S2Z from Newport Corporation of Mountain Valley, California. Ingeneral, the zoom laser-diode line projector system 1 comprises a lineprojector head 2 and a power supply 3. The line projector head 2includes a 1.5 milliwatt laser, and electronic circuitry for regulationof optical power output and protection of the laser diode against linetransients and electromagnetic noise. In addition to having an input formodulation of the laser output, line projector head 2 also includes beamshaping optics for structuring the optical distribution into a planarconfiguration. Mechanical movements are also provided for easyadjustment of the lens for planar beam geometry. Focus adjustment isalso provided to allow the user to control the line width at any desiredstandoff. Line widths as narrow as 0.004 inch are achievable byadjustment of focus control, whereas line length is adjustable bycontrolling beam divergence.

As illustrated in FIGS. 1A and 1B, in vivo imaging is achieved bydirecting at a preselected angle of incidence the essentially planarlaser beam 4 through a cross-sectional portion of ocular tissue 6. Inthe example shown FIG. 1A, the ocular tissue comprises the crystallinelens, whereas in FIG. 1B the ocular tissue comprises cornea 7, anteriorcortex 8, crystalline lens 9 and posterior cortex 10. As illustrated,incident planar laser beam 4 is directed along a line of incidence 50 toilluminate a cross-sectional portion (i.e., light scatter plane) 5 ofthe ocular tissue, thereby causing planar laser beam 4 to be scatteredby molecules in that light scatter plane. Then, at some preselectedangle of scatter, at least a portion of scattered laser light 11 isdetected at an image detection plane 12 so as to form a cross-sectionalimage of the illuminated ocular tissue. As will be described in greaterdetail hereinafter, detection of the cross-sectional scatter image atimage detection plane 12 can be achieved using one of a number of imagedetection techniques.

In order to maintain the eye relatively stationary with respect toplanar illumination beam 4 and image detection plane 12, the patient'shead should be steadied by a conventional chin and forehead rest (notshown). In the steadied position, the patient faces the planar laserbeam, which is oriented at about 45 degrees to the image detection axis,extending perpendicular from the image detection plane.

As shown in FIG. 2, the scattered light is preferably focused throughthe optics of a binocular microscope system 13, so that the user canvisualize the cross-sectional image formed under the illumination ofplanar laser beam 4. Also, as illustrated, a beam splitter 14 isprovided along an optical path in binocular microscope system 13. Thefunction of beam splitter 14 is to split the beam of scattered light 11from the cross-sectional portion of the cornea and crystalline lens, anddirect the produced light beam 15 onto a photo-electronic image detector16 to form a digitized cross-sectional image. Notably, scatter lightbeam 15 is focused by optics 16A to form the cross-sectional image onthe image detection plane of image detector 16.

Preferably, image detector 16 is a charged coupled device (CCD) videocamera comprising an array of photoresponsive units, and is used inconjunction with a laser 2 producing a planar laser beam output having awavelength preferably in the range of 600 to 650 nanometers. With thisarrangement, a digitized cross-sectional image of the ocular tissue canbe produced, while taking advantage of the CCD camera's sensitivity overthis range of wavelengths. Also at the recommended power level of, forexample, 1.5 milliwatts, the retina can be continuously exposed to theplanar laser beam without risk of thermal injury. In such an embodiment,the digitized cross-sectional image consists of a plurality of pixels,each pixel having an intensity value. In a conventional manner, using agrey-scale of 0-255, the intensity of each pixel can be quantized withgreat precision, and so too the optical density of the ocular tissuerepresented by the pixel values comprising the image.

In order to measure the optical density of ocular tissue, such as thecrystalline lens, over particular zones of interest, the video output ofCCD image detector 16 is provided to a conventional image processingcomputer 17 programmed with comprehensive image processing software thatis capable of performing a variety of functions, including, for example,image analysis, image measurement and image processing. Such software iscommercially available from Media Cybernetics, of Silver Springs,Maryland, under the trade name Image-Pro™. Image processing computer 17also includes a video display device 18 for visually displaying theimages acquired at the image detection plane of CCD camera 16.

An example of several types of image analysis that would typically beperformed upon the cross-sectional images, is illustrated in FIG. 4.

As shown, in FIG. 4, digitized image 21 is displayed on video displaydevice 18. A line of analysis 20 is selected, in this particularexample, extending through the entire cross-sectional image 21 of thecornea, anterior cortex, the nucleus and the posterior cortex of thecrystalline lens. Then using the image analysis function ofImage-Pro™software, the luminance profile along the selected analysisline, can be determined and displayed. From the luminance profile,structural transitions and relative optical density in the ocular tissuecan be readily discerned.

By performing histographic analysis within selected areas of interest 22in digitized cross-sectional image 21, it is possible to determine theoptical density of certain portions of the patient's cornea and thus theprecise degree and location of corneal haze. Notably, with a pixel greyscale of 0-255, optical density within ocular tissue can be quantifiedwith the same degree of precision. Together with the constant luminanceover each slit-like cross-section of the planar laser illumination beam4 and the constant sensitivity of photoelectronic image detector 16,consistent cross-sectional images of ocular tissue can be produced andstored in a repeated manner without variation in the measurement ofoptical density. In this way, crosssectional images of a patient'scornea, for example, can be produced, appropriately indexed as tolocation in the eye, and thereafter stored. At a subsequent date after,for example, exposure to corneal haze factors or suitable drug therapyfor corneal haze, additional cross-sectional images can be produced atthe same location within the cornea. Since the image formationconditions of the present invention can be maintained essentiallyconstant during different image formation sessions, meaningfulcomparisons among these images can be made to determine the progress ofthe corneal haze. Also, owing to the constancy of the image formationconditions and the essentially non-diverging flux density along thewidth dimension of the planar illumination beam, images of the corneaalong a number of parallel cross-sections can be formed, stored andcompared to determine the location and degree of corneal haze in thecornea.

By performing image measurement functions of Image-Pro™ software uponthe detected cross-sectional image, the distances between and the areasand perimeters of various ocular structures can be precisely computed ina conventional manner using geometrical techniques. For a discussion onsuch measurements please see Systems of Ophthalmology, Vol. 5,Ophthalmic Optics and Refraction, p. 109, by Duke Elder, published by CVMosby, St. Louis, 1970; and Clinical Visual Optics, p. 331, by Bennettand Rubbett, published by Buttersworth, London, 1984. Such measurementscan be most useful in properly fitting a patient with an intracapsularintraocular lens that fits snugly into the capsular bag without thenecessity of elastic haptics. With the method of the present invention,it is thus possible to precisely determine a patient's crystalline lensspecifications, i.e., exterior and posterior curvature and diameter,thereby allowing the use of a new class of hapticless intraocularlenses.

In order to produce a three-dimensional visual model of ocular tissuesuch as the cornea, either of the ocular tissue analyzing systems shownin FIGS. 5 and 6 can be used. In general, each system produces planarlaser beam 4 for the purpose of illuminating, in a sequential manner, aplurality of parallel cross-sections of ocular tissue. As in thepreviously described embodiment, light scatter 11 from eachcross-section is sequentially detected at the image detector plane,whereupon the detected image is stored or otherwise recorded.Thereafter, the plurality of cross-sectional images are reconstructed ina conventional computer graphics system having three-dimensionalmodeling capabilities. Two-dimensional views of the reconstructed modelcan then be examined along desired viewing directions provided by thecomputer graphics system.

In FIG. 5, ocular tissue analyzing system 30 comprises a platform 31,which is adapted to move along a pair of spaced-apart rails 32A and 32B,which are fixed relative to a stationary base portion (not shown).Preferably, the base portion will be of a height sufficient to permitthe user to view the eye through binocular microscope system 13 mountedabove platform 31 by way of a first support stand 33. A stepper motorand an appropriate gearing mechanism 33A is provided for effectuatingsequential movement of platform 31 relative to rails 32A and 32B andstationary base portion. As illustrated in FIG. 5, planar laser beamsource 1 and binocular microscope system 13 of FIG. 2 are fixedlymounted to platform 31 by way of first and second support stands 33 and34, respectively. Preferably, these support stands are adjustable sothat the optical axes of laser beam source 1 and microscope system 13can be adjusted to lie within substantially the same optical planes.Also, in this embodiment each selected line of incidence of the planarillumination beam and the scatter angle of the image detection plane arefixed at an angle of about 45 degrees.

As in FIG. 2, microscope system 13 of FIGS. 5A and 5B also includes abeam splitter 14 for forming a light scatter beam which is directed ontophotoelectronics image detector 16. As illustrated in FIGS. 5A and 5B,the output of image detector 16 is provided to conventional 3-D computergraphics system 35, which includes video monitor 18, as describedhereinabove. A sequential controller 36 is also provided forsynchronously controlling the movements of platform 31 with respect tostationary base, as well as for transferring detected images from imagedetector 16 to 3-D computer graphics system 35.

At the beginning of an image acquisition process, platform 31 ispositioned so that illumination beam 4 passes through a line ofincidence 50A, co-planar with an end most portion of crystalline lens 9.During the first image acquisition cycle, planar laser beam 4 fromsource 1 is directed into the ocular tissue along line of incidence 50Awhich is substantially parallel to the optical axis of the eye. Alongthis line of incidence, planar laser beam 4 illuminates molecules lyingalong a light scatter plane coplanar with the planar laser beam andscatters the laser light. While under the control of synchronouscontroller 36, image detector 16 detects a portion of the scatteredlaser light which is focused through the optics of image detector 16 toform the scatter image. The scatter image is detected by image detector16 which is positioned at a scatter angle which is fixed with respect tothe selected line of incidence, along which planar laser beam 4propagates. The detected scatter image is then transferred to 3-Dcomputer graphics system 35 for storage. Synchronous controller 36 thenmoves platform 31 a very small lateral increment with respect to theeye, in the direction of the reference arrow 37. This lateraldisplacement permits planar laser beam 4 to be once again directed intothe ocular tissue, but this time along a line of incidence 50B andwithin a light scatter plane which is offset, yet parallel to theprevious line of incidence 50A and corresponding light scatter plane.The detected cross-section image along line of incidence 50B is thentransferred from image detector 19 to 3-D computer graphics system 35for storage.

The above-described process of incrementally moving platform 31 tosequentially offset the line of incidence from the previous line ofincidence and to synchronously acquire, transfer and store the detectedimage, is repeated a number of times under the control of synchronouscontroller 36 until a sufficient number of parallel cross-sectionalimages have been acquired. Thereafter, these images are used to computeone or more reconstructed three-dimensional image of the ocularstructure under examination. Such 3-D image reconstructions can beproduced using conventional programming techniques, then stored inmemory of computer graphics system 35, and subsequently displayed alongdesired or selected viewing directions.

The operation of ocular tissue analysis system 40 is similar in manyrespects to system 30 illustrated in FIGS. 5 and 5A. For example, lasersource 1 and microscope system 13 are fixedly mounted onto a platform 41in a manner described above in connection with the second embodiment.There are several differences, however. Platform 41 is stationary withrespect to the eye of the patient. Also, to laterally displace planarlaser beam 4 with respect to the patient's eye, a glass plate 42 of apredetermined thickness is mounted to a support frame 43. In turn,support frame 43 is supported by a post 44 which is rotatable withrespect to platform 41 by a stepper motor 45 operated under the controlof a synchronous controller 46. As stepper motor 45 is driven bysynchronous controller 46, glass plate 42 is rotated a preselectedamount, thereby effectuating desired incremental lateral displacement ofthe planar laser beam along a selected line of incidence, preferablyparallel with the optical axis of the eye under examination.

At the beginning of the image acquisition process, refractive plate 42is preferably substantially perpendicular with planar illumination beam4. During the first image acquisition cycle, the refractive plate 42remains in its original or initial position, and the end mostcross-section of ocular tissue is illuminated and the scatter imagedetected by image detector 16. After synchronously transferring thefirst detected image to the 3-D computer graphics system 35 undercontrol of synchronous controller 46, refractive plate 42 is rotated bya small angular increment to displace slightly the line of incidence ofplanar illumination beam 4 away from the previously selected line ofincidence. A cross-section of ocular tissue parallel to its firstcross-section (i.e., light scatter plane) is thus illuminated and thescattered light is detected by image detector 16, whereupon this secondcross-sectional image is transferred to 3-D computer graphics system 35for storage. The above image acquisition cycle is repeated a number oftimes under the control of synchronous controller 46 until a sufficientnumber of images are acquired for 3-D image reconstruction of the corneaof a particular patient, as discussed above.

By performing image measurement functions upon the data represented inthe 3-D image reconstruction (i.e., model) of the cornea, severalimportant types of data can be precisely obtained. For example, thethickness of the cornea at any point on the surfaces thereof can becomputed and provided as digitized data output correlated with a pointon the surface thereof. Also, topographical data regarding the surfacecharacteristics of the patient's cornea (i.e. corneal curvature) priorto laser surgery can be precisely computed and provided as data outputin a suitable format. Such corneal thickness data and topographical datacan be then used by the ophthalmological surgeon in determining the newsurface profile to be sculptured in the stroma tissue of the cornea of aparticular patient, in order to achieve a desired degree of opticalcorrection in his or her eye. Details regarding the computation of suchtypes of data from 3-D image reconstructions of the cornea can be foundin the publication entitled "Computerized Surface Reconstruction ForCorneal Topography And Pachymetry Using Digitized Slit-Lamp VideoImages", by J.H. Hoffman, et al., Arvo Abstract Paper No. 1512-69 (1992).

In the illustrated embodiments, photoelectronic image detectingapparatus and digital image processing techniques are utilized incarrying out the present invention. However, photographic imagerecording techniques and optical density measurement techniques forphotographic images may also be used to carry out the present inventionwith expectedly good results.

While the particular embodiments shown and described above have provento be useful in many applications in the ophthalmic art, furthermodifications of the present invention herein disclosed will occur topersons skilled in the art to which the present invention pertains, andall such modifications are deemed to be within the scope and spirit ofthe present invention defined by the appended claims.

What is claimed is:
 1. A method for in vivo imaging of corneal tissue,comprising the steps:(a) providing a laser beam having a substantiallyplanar configuration; (b) directing said laser beam through across-sectional portion of said corneal tissue, so as to illuminate saidcross-sectional portion and cause said laser beam to be scattered bymolecules in said corneal tissue; and (c) detecting at least a portionof said scattered laser light so as to form a cross-sectional image ofsaid corneal tissue.
 2. A method of claim 1, wherein step (a) comprisesproviding a laser beam having a substantially planar configuration and aslit-like cross-sectional dimension of a substantially uniformluminance.
 3. The method of claim 1, which further comprises(d)analyzing said cross-sectional image of said corneal tissue, anddetermining optical properties of said cross-sectional portion ofcorneal tissue, said optical properties including corneal haze in saidcorneal tissue.
 4. The method of claim 1, wherein step (c) comprisesforming a digitized cross-sectional image of said corneal tissue, saiddigitized cross-sectional image consisting of a plurality of pixels,each said pixel having an intensity value.
 5. The method of claim 4,wherein step (d) comprises analyzing at least a region of said digitizedcross-sectional image by processing the intensity values of the pixelsrepresenting said region.
 6. The method of claim 4, wherein saiddigitized cross-sectional image is formed by focusing said portion ofscattered light onto an image detecting array of photo-responsiveelements.
 7. The method of claim 6, wherein step (a) comprisesgenerating from a laser, said laser beam having a wavelength in therange of about 600 to about 650 nanometers, and step (c) comprisesdetecting said cross-sectional image on said image detecting arraycomprising a plurality of operationally associated charge coupleddevices.
 8. The method of claim 7, wherein step (a) comprises producinga laser beam from a lasing device and guiding said laser beam through atelescoping optical system to produce said laser beam.
 9. The method ofclaim 1, wherein step (b) comprises directing said laser beam through across-sectional portion of the cornea in a human eye, so as toilluminate said cross-sectional portion and cause said planar laser beamto be scattered by molecules in said cornea, and wherein step (c)comprises detecting at least a portion of said scattered laser light soas to form a cross-sectional image of said cornea.
 10. The method ofclaim 1 which further comprises forming a plurality of cross-sectionalimages of said corneal tissue, each said cross-sectional image beingspecified at a different light scatter plane defined within said cornealtissue.
 11. The method of claim 10, which further comprises forming athree-dimensional image of said corneal tissue on the basis of saidplurality of said cross-sectional images.
 12. The method of claim 11,wherein each said cross-sectional image is formed bydirecting said laserbeam into said corneal tissue, at a selected line of incidence withrespect to said corneal tissue so that, for each said selected line ofincidence, said laser light scatters principally in a single lightscatter plane within said corneal tissue, and detecting a portion ofsaid scattered laser light from said single light scatter plane, at afixed angle of scatter with respect to said selected line of incidence.13. The method of claim 11, wherein each said cross-sectional image isformed bydirecting said laser beam into said corneal tissue at selectedline of incidence with respect to said corneal tissue so that, for eachsaid selected line of incidence, said laser light scatters principallyin a different light scatter plane within said corneal tissue, anddetecting a portion of scattered laser light from each said differentlight scatter plane, at a scatter angle which is fixed with respect tosaid selected line of incidence, wherein each said line of incidence isselected by repositioning together means used for directing said laserbeam and for detecting said scattered laser light.
 14. A method for invivo imaging of corneal tissue, comprising the steps:(a) providing alaser beam having a substantially planar configuration; (b) directingsaid laser beam through a cross-sectional portion of said cornealtissue, so as to illuminate said cross-sectional portion and cause saidlaser beam to be scattered by molecules in said corneal tissue; (c)detecting at least a portion of said scattered laser light so as to forma plurality of cross-sectional images of said corneal tissue, each saidcross-sectional image being specified at a different light scatter planedefined within said corneal tissue; (d) forming a three-dimensionalimage of said corneal tissue on the basis of said plurality of saidcross-sectional images; and (e) using said three-dimensional image todetermine the thickness of said cornea along a selected cross-section ofsaid cornea.
 15. A method for in vivo imaging of corneal tissue,comprising the steps:(a) providing a laser beam having a substantiallyplanar configuration; (b) directing said laser beam through across-sectional portion of said corneal tissue, so as to illuminate saidcross-sectional portion and cause said laser beam to be scattered bymolecules in said corneal tissue; (c) detecting at least a portion ofsaid scattered laser light so as to form a plurality of cross-sectionalimages of said corneal tissue, each said cross-sectional image beingspecified at a different light scatter plane defined within said cornealtissue; (d) forming a three-dimensional image of said corneal tissue onthe basis of said plurality of said cross-sectional images; and (e)using said three-dimensional image so as to determine the topography ofsaid cornea.
 16. Apparatus for in vivo imaging of corneal tissue,comprising:laser beam provision means for providing a planar laser beamhaving a substantially planar configuration; laser beam directing meansfor directing said laser beam through a cross-sectional portion of saidcorneal tissue, and cause said laser beam to be scattered by moleculesin said corneal tissue; and image detection means for detecting at leasta portion of said scattered laser light so as to form a cross-sectionalimage of said corneal tissue.
 17. The apparatus of claim 16, whichfurther comprises analyzer means for analyzing said detectedcross-sectional image of said corneal tissue, and determining opticalproperties of said corneal tissue, at said cross-section portion. 18.The apparatus of claim 17, wherein said image detection means comprisesan image detecting array capable of forming a digitized cross-sectionalimage of said corneal tissue, said digitized cross-sectional imageconsisting of a plurality of pixels, each said pixel having an intensityvalue.
 19. The apparatus of claim 18, wherein said analyzer means iscapable of analyzing at least a region of digitized cross-sectionalimage by processing the intensity values of the pixels representing saidregion.
 20. The apparatus of claim 16, wherein said laser beam provisionmeans comprises a laser and an optical system, said laser producing alaser beam which is focused by said optical system to produce saidsubstantially planar laser beam.
 21. The apparatus of claim 16, whichfurther comprises means for forming a plurality of cross-sectionalimages of said corneal tissue, each said cross-sectional image beingspecified at a different light scatter plane defined within said cornealtissue.
 22. The apparatus of claim 21, which further comprises threedimensional image forming means for forming a three-dimensional image ofsaid corneal tissue on the basis of said plurality of saidcross-sectional image.
 23. The apparatus of claim 21, wherein said threedimensional image forming means comprisesdirecting means for directingsaid laser beam into said corneal tissue, at a selected line ofincidence with respect to said corneal tissue, so that, for each saidselected line of incidence, said laser light scatters principally in adifferent light scatter plane within said corneal tissue, and detectingmeans for detecting a portion of said scattered laser light from saiddifferent light scatter plane, at a fixed angle of scatter with respectto said selected line of incidence.
 24. The apparatus of claim 21,wherein said three-dimensional image forming means comprisesdirectingmeans for directing said laser beam into said corneal tissue at aselected line of incidence with respect to said corneal tissue so that,for each said selected line of incidence, said laser light scatterprincipally in a different light scatter plane within said cornealtissue, detecting means for detecting a portion of scattered laser lightfrom each said different light scatter plane, at a scatter angle whichis fixed with respect to said selected line of incidence, andpositioning means for positioning together said directing means and saiddetecting means so that each said line of incidence can be selectedwhile maintaining said scatter angle fixed with respect to said selectedline of incidence.
 25. Apparatus for in vivo imaging of corneal tissue,comprising:laser beam provision means for providing a planar laser beamhaving a substantially planar configuration; laser beam directing meansfor directing said laser beam through a cross-sectional portion of saidcorneal tissue, and cause said laser beam to be scattered by moleculesin said corneal tissue; means for detecting at least a portion of saidscattered laser light and for forming a plurality of cross-sectionalimages of said corneal tissue, each said cross-sectional image beingspecified at a different light scatter plane defined within said cornealtissue; means for forming a three-dimensional image of said cornealtissue on the basis of said plurality of said cross-sectional image; andmeans for determining the thickness of said cornea along a selectedcross-section of said cornea using said three-dimensional image. 26.Apparatus for in vivo imaging of corneal tissue, comprising:laser beamprovision means for providing a planar laser beam having a substantiallyplanar configuration; laser beam directing means for directing saidlaser beam through a cross-sectional portion of said corneal tissue, andcause said laser beam to be scattered by molecules in said cornealtissue; means for detecting at least a portion of said scattered laserlight forming a plurality of cross-sectional images of said cornealtissue, each said cross-sectional image being specified at a differentlight scatter plane defined within said corneal tissue; means forforming a three-dimensional image of said corneal tissue on the basis ofsaid plurality of said cross-sectional image; and means for determiningthe topography of said cornea along a selected cross-section of saidcornea using said three-dimensional image.